Newborns of many altricial mammalian species must identify their mother through the use of learned olfactory cues in order to survive. This early olfactory learning is associated with large functional and structural changes within the olfactory bulb in infant rats. Based on recently completed work, it appears that centrifugal projections from the brainstem to the olfactory bulb may be involved in both the behavioral and neural changes associated with olfactory learning. These projections contain norepinephrine (NE) and serotonin (5-HT). Extensive evidence has already linked both NE and 5-HT activity with sensory processing and arousal, and NE is known to play a modulatory role in neural development and memory formation. The goal of the proposed research is to understand the mechanisms underlying the acquisition of the behavioral and neural responses following olfactory classical conditioning in infant rats. Specifically, the role of olfactory bulb NE and 5-HT in neonatal olfactory learning will be assessed.